The present invention describes a novel class of materials that fits between the ordinary industrial laminates and research-type nanolaminates or superlattices, in regards to properties and cost. The novel Interface-Defined nano-Laminated materials (IDnL) of this invention differ from both the large-scale laminates and the extremely fine-scale superlattices, due to their unique micro- and nano-structures produced by the novel methods of fabrication, which are also a subject of this invention. In the new IDnL materials, the interfaces between the alternative layers can be designed and fabricated from many different materials. Also, these interfaces have unique properties and structures, which can be varied from nearly coherent to completely incoherent by varying the processing approach. The degree of deviation from perfect coherency at the interfaces potentially can be controlled without much increase in cost of the IDnL materials. Thus, IDnL materials and the novel methods of their preparation potentially can be used in a wide range of industrial applications, from those of the relatively coarse structural laminates, to those of the extremely fine electronic, semiconducting, and optical nanolaminates.
In general, laminates can be made with layers having a wide range of thickness. The terms ‘laminated materials’, or ‘laminates’, generally refer to materials that consist of many parallel layers of relatively thick (layer thickness>1 mm) dissimilar materials. Laminates are utilized in many diverse fields, such as food preparation (French and German pastry), penetration-resistant materials (armor, bullet-proof glass), heat shields for satellites (NASA, DOD), as well as tools (metal cutting inserts), and weapons (Japanese samurai swords)—just to name a few.
The properties of laminates, in general, are controlled by two factors, i.e. the properties of the material within the layers and the properties of the interfaces between the layers. When the number of layers is small (in this case a material usually referred to as ‘layered’), it is predominately the properties of the materials within the individual layers that define the properties of the whole laminate. However, as the number of layers increases, the properties of the interfaces between the dissimilar layers begin to impose an ever increasing effect on the properties of the laminate. In some applications, it is the properties of the interfaces that are the determining factor in the performance of the whole laminate. For example, a reflecting insulator that consists of a number of metallic layers, each of which is an excellent conductor of heat and is separated from the next reflector by an air gap or vacuum, is, nevertheless, an excellent insulator because of the reflection and scattering of heat perpendicular to the metal/gas interfaces.
Laminates have many industrially-useful properties. The properties of laminates are anisotropic, so they are often called ‘2-dimensional materials’, because their properties in the plane of the layers and perpendicular to that plane are drastically different. For example, heat conductivity in the crystal plane and perpendicular to the crystal planes of pyrolytic graphite can differ by three orders of magnitude; fracturing goes easily along the glass planes in laminated glass, but is quickly arrested in the direction perpendicular to the glass planes; electrical current propagates in planes, but not perpendicular to the planes in metal/oxide laminates utilized in super-capacitors, etc.
The anisotropic properties of laminates can be highly useful in impeding conduction of heat as well as propagation of fracture, or chemical attack. Regardless of the form of the propagating entity, laminate materials usually inhibit propagation of the energy or matter in the direction perpendicular to the layers, while dissipating this energy or matter principally along the surface of the interfaces.
In contrast to the laminates with macroscopic thick layers discussed above are the conventional nanolaminated materials and superlattices that have been researched extensively since the late 1970s. These are extremely finely-layered materials with the thickness of individual layers of the order of 1 to 10 nm. They are also prohibitively expensive for industrial applications (except for some high-tech uses that require very small samples, such as reading heads in magnetic storage). The word ‘superlattice’ was coined by physicists, who were the early investigators of these materials, to emphasize the existence of extra peaks in X-ray diffraction patterns of these materials. Traditionally, the word ‘superlattice’ is used with nanolayered materials that have coherent interfaces, i.e. when the lattice planes are continuous from one phase to another across the interface. When the interfaces are incoherent, the material is usually referred to as ‘nanolayered’. (In the instant invention, the word ‘nanolaminate’ will be used for all these types of materials with layers of nanometer thickness up to 999 nanometers.) These nano-laminated materials have been found to have very intriguing and industrially-useful properties. The whole area is still an active research field in Materials Science and Physics. Electronic, magnetic, and mechanical properties of these materials are still actively researched, scientific conferences held, and new applications come out every year. New important properties, such as superior hardness/toughness combination, excellent wear resistance, super-modulus effects, superconductivity, optical waveguide properties, and magnetic properties are active areas of research in conventional nano-laminates.
Presently, despite their attractive properties, from the point of view of industrial and commercial applications, conventional nano-laminates have some very serious drawbacks. That is, to manufacture these materials currently requires very expensive equipment, very clean conditions, and high vacuum, as the nanolaminates are essentially built-up one atom at a time. To date, these materials have been fabricated utilizing magnetron sputtering or atomic layer deposition (ALD). Nanolaminates manufactured by these techniques usually have strongly-attached coherent interfaces, because of the perfection of the deposition and atomic uniformity of the interface. However, the size of these materials is limited, and the cost to make commercial products with these techniques is prohibitive with state-of-the art techniques.
The desired degree of coherency at each interface depends on the application. As stated above, laminate materials usually inhibit propagation of the energy or matter in the direction perpendicular to the layers, while dissipating this energy or matter along the surface of the interfaces. Thus, to inhibit the propagation of energy, such as thermal energy or crack propagation perpendicular to the interfaces, it is desirable to have an incoherent interface between the layers of the laminate because coherent interfaces do not effectively scatter the energy perpendicular to them.
Laminates with coherent interfaces have very useful properties such as conductivity, as well as enhanced bonding and minimum distortion across the interface which leads to applications in ionic conductors, semiconductors and optics as will be described below. While taking advantage of these properties, it is necessary to realize that laminates with coherent interfaces such as metallic superlattices are usually quite brittle.
In addition, coherency at the interfaces leads to poor thermal stability, thus most superlattices are unstable even at room temperatures, and quickly interdiffuse, losing their nanoscopic properties at or just above ambient temperatures. For these reasons, coherency at the interfaces of nanolayered materials is not always a desirable quality and some departure from coherency is often desired to assure stability at elevated temperatures and improved mechanical properties. Such departures from ideal coherency are often induced by raising the temperature of the substrate or the rate of deposition during the magnetron-assisted sputtering of nanolaminates.
Because of the low thermal stability and high cost, conventional nanolaminates are mainly used in high-tech-type industries, where the price of the product justifies the expense of making a material one layer at a time at the ‘breath-taking’ rate of 1 micron/hour. The fabrication methods currently used for making nanolaminates cannot be scaled-up to industrially meaningful dimensions because they are inherently prohibitively expensive.
Thus, a need exists for an industrially-scalable batch or continuous technique to produce low-cost nanolaminates at a cost of at least an order of magnitude and preferably at least two orders of magnitude lower than is currently possible with the state-of-the-art techniques. In addition, a need exists to be able to produce nanolaminates of much higher areas. That is, a need exists for a process that is able to fabricate a low-porosity nanolaminate material, in which each interface has a cross-sectional area of at least 0.1 square meter, preferably 1 square meter, and most preferably 10 square meters. The instant invention achieves the goal of providing an industrially-scalable methodology for fabricating large-area parts from nanolayered materials, which are already known in scientific research. Moreover, in the process of developing this methodology, the inventors have discovered a new class of nano-layered materials, termed IDnL, which cover the range of layer thickness between ordinary laminates and superlattices, as outlined above. These new materials have micro- and nanostructure very different from that of the two classes of laminated materials discussed above. Because these materials are fabricated from powders, which are eventually densified and consolidated via rapid sintering, hot rolling, dynamic compaction, plastic deformation and such, the new materials have properties different from that of the already known laminated materials.
There are a lot of approaches, methods, and techniques that have been employed for making metal and ceramic laminates. The simplest approaches produce layers at least 100 microns in thickness and involve placing one layer on top of the other, which can be done by dipping in or painting wet slurries as well as by utilizing tapes. Other techniques that are able to deposit layer by layer, one after another, utilize chemical, physical, mechanical, explosive, or high-voltage approaches to deposit material on surfaces. Techniques that can produce micron-thick layers include ink-jet printing, silk-screen printing, plasma spraying, and the use of a Meyer bar or a Doctor blade. The thinnest nanometer-thick layers require the use of techniques, such as, chemical vapor deposition, physical vapor deposition, atomic layer deposition, pulsed laser deposition, electro-deposition, as well as magnetically and electrostatically-assisted sputtering in which layers are built-up one atom at a time. Other techniques, such as electrophoresis have been used to deposit ceramic nano-laminates from aqueous suspensions. All of the above techniques are inherently very slow not only because of the low rate of deposition but also because of the need to move the substrate between deposition stations or to change the precursor between layer depositions, as well as to allow the previous layer to dry or cure before the next layer can be applied.
Although these techniques can produce a nano-laminate material with essentially an unlimited number of layers, they cannot do this on very large samples at a reasonable cost due to precursor cost, equipment cost, or the cost of sequential deposition of thousands of layers of different materials. These techniques are more applicable to fabricating layered coatings. Considering these factors, it would be prohibitively expensive to fabricate bulk parts with at least a square meter in area and 100,000 layers in thickness.
A few methods to make bulk nano-layered materials do exist, however. One such method is used in manufacturing exfoliated graphite, vermiculate, and mica-type thermal insulation. This method utilizes the natural property of these materials to form flakes. The individual flakes whose area varies from sub-micron to hundreds of millimeters are dispersed in a liquid. When the liquid is removed by evaporation, the flakes settle and form a nano-layered material. However, the individual layers in such structures are not continuous or uniform and the thickness cannot be easily controlled. In addition, it is impossible to make multi-component nano-layered materials, i.e. nano-laminates with neighboring layers having different composition or structure, with a nanometer layer thickness employing this technique.
A multiple extrusion step approach has been utilized in the electronics industry for more than 50 years to make nanometer thick layers in Channeltron photo-multiplier tubes. In this process, sacrificial glass rods coated with a different glass are bundled together in a hexagonal array and drawn down to a very small diameter through many drawing steps. After the sacrificial glass is removed, micron sized holes separated by nanometer thick walls formed by the coating remain. A similar process is currently used in superconductor wire processing to make fibers that consist of large number of closely packed cores. In this case, ceramic superconductor wires are assembled in a closely-packed bunch within a copper outer tube and then extruded to ever smaller diameter tubes to make thin wires that consist of thousands of thin electrically-isolated superconducting wires. These approaches are conceptually similar to the current invention, however these approaches are directed towards making single layer 1-dimensional structures—tubes and wires-not 2-dimensional multi-layered bulk materials as in this invention.
To summarize the prior art, no approaches exist in the current state-of-the-art for making large quantities of low-cost high-surface-area nano-laminates with at least one hundred thousand continuous nanometer-thick layers per 1 cm of thickness of the laminate with each layer having continuous unbroken interfaces between different materials, such as metals, ceramics, semiconductors, or other materials. Not only can the instant invention achieve these goals, but it can do so in an economical, industrially-scalable manner.